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Lenz's law
Intermediate
Induced current opposes the change causing it.
The induced current's magnetic effect opposes the change that created it. It's conservation of energy: otherwise you'd get free energy.
Dropping a magnet through a copper tube slows it.
It opposes the change, not the flux itself.
In more detail
Lenz's law states that the induced current flows in the direction that opposes the change in flux that produced it. It is a consequence of energy conservation.
Real-world uses
- Magnetic braking systems use Lenz's law to slow moving parts.
- Induction heating and damping rely on opposing currents.
- Eddy current brakes and induction cookers work because induced currents oppose the change that creates them.
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Frequently asked questions
Why must it oppose the change?
If the induced current aided the change, energy would be created from nothing.
How do I apply it?
Find the direction of flux change and choose the induced current that produces opposing flux.
Why is Lenz's law the sign in Faraday's law?
It shows that the induced current creates a field which opposes the change, which is a consequence of energy conservation.
Related topics in Magnetism & Induction
Permanent magnets · Magnetic flux · Faraday's law · Motional emf · Eddy currents · Eddy current braking